Technical Note: A Protocol to Preserve the Dural Safety Margin During Simultaneous Hybrid Lumbar Unilateral Biportal Endoscopy and Cervical Laminoplasty

Simultaneous single-stage decompression for tandem spinal stenosis (TSS) is increasingly favored to reduce recovery time [1, 2]. The "hybrid" approach combines open cervical laminoplasty with lumbar Unilateral Biportal Endoscopy (UBE). However, UBE requires continuous saline irrigation [3], which creates hydrostatic pressure capable of increasing intracranial pressure via the subarachnoid space [4, 5]. We hypothesized this transmitted pressure impacts the exposed cervical dura during simultaneous surgery, posing an iatrogenic risk. We retrospectively reviewed three consecutive TSS cases treated with simultaneous open cervical laminoplasty and lumbar UBE. In the index case, continuous lumbar irrigation was maintained during cervical decompression. Following observed complications, we implemented a "Stop-Flow Protocol" for subsequent cases, pausing lumbar irrigation during critical cervical maneuvers. In Case 1, active lumbar irrigation (40 mmHg) caused significant cervical dural bulging, contributing to an incidental durotomy while preparing the laminoplasty opening. This was attributed to the Hydraulic Coupling effect of transmitted pressure [5]. In Cases 2 and 3, utilizing the "Stop-Flow Protocol" (pausing inflow, opening outflow), the cervical dura remained relaxed. No further dural injuries occurred, and all patients achieved good clinical outcomes. Simultaneous hybrid surgery makes the cervical dura susceptible to injury due to hydraulic coupling. Hydrostatic pressure from lumbar irrigation causes cervical dural bulging, increasing iatrogenic durotomy risk. Surgeons must coordinate to pause lumbar irrigation during critical cervical manipulation to ensure dural relaxation [10].